http://www.aviation-news.co.uk 61high-energy boron compounds to achieve
the same 750-mile (1,207km) supersonic
dash capability. President John F Kennedy
cancelled WS-125A, having realised that
the West’s estimate of Soviet bomber
numbers was exaggerated. WS-110A lived
on, in parallel with North American Aviation’s
(NAA) Mach 3 F-108 Rapier ghter project,
which shared much WS-110A technology.
WS-110A then took some strange forms.
Early studies envisaged a vast machine
weighing 750,000lb (340,194kg) with
‘ oating, disposable wing panels’ containing
fuel, each of which spanned 76ft (23m) and
weighed 191,000lb (86,636kg) but these
were jettisoned before the supersonic dash
stage. Spanning 270ft (82m) in all, with a
209ft (63.7m) fuselage, this behemoth would
have been piloted via a cockpit periscope and
own from specially widened, strengthened
runways. Dismissed as a ‘three-ship
formation’ by LeMay this far-fetched notion
gave way to a fresh series of designs by
Boeing and North American using between
two and six engines and a variety of wing
plan forms and canard fore-planes.SURFING THE COMPRESSION
WAVE
By 1957 both manufacturers had settled
on fairly rm designs; the Model 804-4 for
Boeing which in the end came to nothing
while the WS-110A morphed into the XB-70.
Whereas Boeing employed its usual under-
wing podded engines, the NAA aircraft relied
on internal powerplants and the recently
established principle of ‘compression lift’ tohelp in overcoming drag thereby increasing
the range of a supersonic dash. Essentially,
this involved designing a fuselage and air
intake con guration that maintained an area
of high air pressure beneath the body of the
aircraft and behind the shock wave created by
supersonic ight.
Six engines were placed in a box-like
structure that comprised most of the rear
fuselage and incorporated a wedge-shaped
front edge to its twin intakes, which shaped
and slowed the shock wave as it moved
towards the engines. A high-mounted delta
wing, with tips that folded down at high Mach,
helped to maintain the pressure ‘compression
eld’ beneath the aircraft, increasing lift and
adding to the range.
Designers devoted much time to devising
internal ramps and by-pass doors in the
long, cavernous intakes to manage the
shock waves and air pressure throughout the
intended speed range. When a high-mounted
canard was added to the aircraft’s nose,
the machine’s ‘hooded cobra’ appearance
became very evident.
In de ning WS-110A in 1958 the USAF
wanted Mach 3 speed, altitudes approaching
80,000ft and an atom-bomb payload of
20,000lb (907kg) carried over 6,873 miles
(11,061km). It was an incredibly demanding
speci cation.
Self-defence suggestions included
rearward-launched, ying saucer-shaped
exploding infrared decoy missiles, a rotary
cannon ring pellets full of corrosive
chemicals, or conventional air-to-air missiles
as well as a massive ECM package.Eventually the aircraft’s speed was seen as
its main defence. The project was designated
XB-70 in February 1958 and T/Sgt Francis
Seller won a naming competition with his
suggestion of ‘Valkyrie’ (after the mythical,
beautiful female Norse warriors) for the
bomber, which was then scheduled to enter
service in 1964.
In an extremely short design period,
compared with the decades required by
today’s combat aircraft, North American
engineers devised a ground-breaking
airframe with a moveable ramp to cover
the windshield at supersonic speeds, twin
all-moving vertical ns, downward-hinged
outer wing panels to increase stability and
compression and ve ‘elevons’ to replace
conventional ailerons and elevators.
A 14ft (4.26m) long weapons bay was
located between the 7ft (2.13m) high intake
tunnels and, after consideration of the Pratt
& Whitney J58 engine (later used in the
Lockheed SR-71) the General Electric YJ93-
GE-3 turbojets, each developing 29,300 lbs of
thrust, was chosen for the XB-70 and F-108.
Six were installed in parallel bays in the rear
fuselage.
Fighting constant threats of cancellation as
costs rose and political opposition (including
that of President Dwight D Eisenhower)
increasingly favoured the missile-plus-Boeing
B-52 option, the programme was cut to a
single research prototype on December 1,- Pressure from USAF generals re-
instated plans for 12 development aircraft in
1960 with assured funding for two XB-70s
and a YB-70 pre-production example. The
The Valkyrie’s most predatory
pose could be seen at high
altitude, cruising with the
wing tips lowered. NASA60-65_xb70DC.mfDC.mfDC.indd 61 02/05/2018 12:35